1. Field of the Invention
The invention relates to a reactor for anaerobically purifying waste water, especially waste water from the paper industry, comprising a reactor vessel, several inlets arranged in the bottom region of the reactor vessel to feed waste water to be purified into the reactor, at least one outlet for discharging purified water, and at least one sediment drain, whereby one or more inlets are fed by one supply pipe and several supply pipes are fed by one collecting supply pipe.
The invention moreover relates to a method for anaerobically purifying waste water, especially waste water from the paper industry, comprising a reactor vessel, several inlets arranged in the bottom region of the reactor vessel to feed waste water to be purified into the reactor, at least one outlet for discharging purified water, and at least one sediment drain, whereby one or more inlets are fed by one supply pipe and several supply pipes are fed by one collecting supply pipe.
2. Description of the Related Art
A multitude of mechanical, chemical and biological methods and corresponding reactors are known for purification of waste water. In biological waste water purification, the waste water to be purified is brought into contact with aerobic or anaerobic micro-organisms which, in the case of aerobic micro-organisms decompose organic contaminants contained in the waste water predominantly to carbon dioxide, biomass and water, and in the case of anaerobic micro-organisms mainly to carbon dioxide and methane and only in small part to biomass.
In recent times the biological waste water purification methods are hereby carried out increasingly with anaerobic micro-organisms, since with the anaerobic waste water purification oxygen does not have to be fed with high energy expenditure into the bioreactor; energy-rich biogas is produced during purification which can subsequently be utilized for generating of energy; and substantially lower volumes of excess sludge are produced.
Depending on the type and form of the utilized biomass, the reactors for anaerobic waste water purification are categorized into contact sludge reactors, UASA-reactors, EGSB-reactors, fixed bed reactors and fluidized bed reactors.
Whereas the micro-organisms in fixed bed reactors adhere to stationary carrier materials and the micro-organisms in fluidized bed reactors adhere to freely moving, small carrier material, the micro-organisms in UASB and EGSB reactors are utilized in the form of so-called pellets. In contrast to UASB (upflow anaerobic sludge bed) reactors, EGSB (expanded granular sludge bed) reactors are higher and at same volume have a substantially smaller base area.
In the case of UASB and EGSB reactors, waste water which is to be purified, or a mixture of waste water which is to be purified and already purified waste water from the outlet of the anaerobic reactor is fed continuously to the reactor through an inlet which is arranged in the lower region of the reactor and is directed through a micro-organism pellet-containing sludge bed which is located above the inlet.
During decomposition of the organic compounds from the waste water, the micro-organisms form in particular methane and carbon dioxide containing gas (which is also referred to as biogas) which partially adheres to the micro-organism pellets in the form of small bubbles and which partially rises to the top in the reactor in the form of free gas bubbles. Because of the added gas bubbles the specific weight of the pellets decreases, which is the reason that the pellets rise to the top in the reactor. In order to separate the formed biogas and the rising pellets from the water, separators are arranged in the center and/or upper part of the reactor, mostly in the embodiment of gas hoods under the top of which biogas accumulates, forming gas cushions. Purified water, relieved of gas and micro-organism pellets rises to the top in the reactor and is drawn off at the upper end of the reactor through overflows. Methods and associated reactors are described for example from EP 0170 332 A and EP 1 071 636 B.
For the previously described methods uniform distribution of the waste water added to the reactor through the inlet across the reactor cross section is particularly important in order to achieve good blending of the sludge pellets which are present in the reactor, of the water which is present in the reactor and of the added waste water. In order to meet these requirements, a multitude of reactors, equipped with appropriate inlet distributors have already been suggested.
These have a multitude of inlets in the region of the reactor chamber through which the waste water which is to be purified is to be distributed.
Especially with waste water having high lime content, such as waste water from the paper industry, precipitation and sediment deposits occur frequently. These settle on the bottom of the reactor vessel and thereby increase the flow resistance at the discharge openings of the inlets. The result is that a greater volume flows from other inlets of the inlet distributor.
This may result in that more than 75% of the inlets are inactive without this being recognizable from the outside. Because of the non-uniform supply of waste water associated with this, the efficiency of the waste water treatment can be substantially lowered.
What is needed in the art is to ensure an as uniform as possible infeed of waste water to be purified at the bottom of the reactor vessel. In the following the term “pellets” is to be understood to be in particular granulated bio-sludge.